Project Summary: This proposal studies how a key cytoplasmic innate immune receptor, NOD2, contributes to renal ischemia reperfusion (IR) injury. The project is highly significant for ischemic kidney injury, as occurs frequently in hospitalized patients. Broad/long-term objectives: The long-term goals of the proposed research are to define how NOD2 contributes to injurious tissue responses in the kidney. Specific Aims: The specific objective of this proposal is to test the hypothesis that the cytoplasmic pattern recognition receptor NOD2 is a key contributor to renal tubular epithelial damage induced by renal IR injury. Aim 1 asks whether NOD2 activation directs renal tubular epithelial cell injury, defines the signaling events that lead to this injury, and determines whether NOD2 blockade prevents renal tubular epithelial injury. Aim 2 asks whether activation of NOD2 contributes to ischemic renal injury primarily through direct (local) or indirect (systemic) mechanisms. Research Design and Methods for Achieving the Stated Goals: Aim 1 will test how ligation of NOD2 injures renal tubular epithelial cells, whether the NOD2 activating stimulus directs the mode of RTE cell injury, how molecules released from necrotic cells (DAMPs) activate NOD2-mediated injury of healthy RTE cells, and whether RTE cell injury can be blocked by either blocking NOD2 or one of its upstream activating pathways. In vivo IR injury incorporates other mediators of tissue injury, such as inflammation, so aim 2 focus on whether NOD2 activation plays a broader role in the kidney by separating local (kidney injury) from systemic (inflammation). Direct (local, kidney specific) effects are separated from indirect (systemic) effects in a kidney transplant model where injury responses of the NOD2-/- transplanted kidney are studied in a wild type (WT) host, and WT kidney injury studied in a NOD2-/- host. Health Relatedness of Project: If the aims of this proposal are met we will learn how molecules released from injured tissue activate NOD2-dependent injurious responses in the kidney. This knowledge is crucial for the development of rational target therapies for prevention or amelioration of renal IR injury in clinical situations where hypoxia is anticipated. Focusing on the earliest events of ischemic kidney injury holds the greatest promise for effective therapeutic strategies.